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Effects of pH on Metals Precipitation and Sorption

Field Bioremediation and Geochemical Modeling Approaches

Department of Geology and Geography, 210 Petrie Hall, Auburn University, Auburn, AL 36849

View larger version (33K): [in a new window]   Fig. 1. Observed (a) Pb and (b) Cd plumes at Troy site in 1998. Also shown are locations of Injection Wells NW3 and NW12. Groundwater generally discharges in the southeast direction toward a wetland.

View larger version (34K): [in a new window]   Fig. 2. Changes in geochemical parameters with time during the first injection experiment after the injection of sucrose and diammonium phosphate solution. (a) pH and Eh vs. time, (b) chalcophile elements (Zn, Cu, Cd, Pb) vs. time, (c) Fe and Eh vs. time, (d) siderophile elements (Ni, Co, V, Cr, As) vs. time, (e) redox-sensitive elements (U and Se) vs. time, and (f) Al and pH vs. time.

View larger version (16K): [in a new window]   Fig. 3. Changes in chalcophile elements vs. time in the second injection experiment.

View larger version (21K): [in a new window]   Fig. 4. Sulfur isotopic composition of dissolved sulfate concentration vs. sulfate concentration during bioremediation experiment.

View larger version (40K): [in a new window]   Fig. 5. Energy dispersive x-ray (EDAX) spectra of filtered materials from groundwater after bacteria sulfate reduction began.

View larger version (19K): [in a new window]   Fig. 6. Predictive cumulative mineral assemblage precipitated as Eh decreases as a result of bacteria sulfate reduction.

View larger version (29K): [in a new window]   Fig. 7. Predictions of the amounts of metals present initially in contaminated water that sorb onto hydrous ferric hydroxides as a function of pH, calculated according to the Dzombak and Morel (1990) surface complexation model.

View larger version (18K): [in a new window]   Fig. 8. Calculated mass of predominant As species of a reaction path in which arsenite sorbs onto ferric hydroxide to form FeH2AsO3 complexes as pH increases. The value of pH increases as a result of bacteria sulfate reduction. Arsenite later desorbs to form AsS complexes under reducing, neutral pH conditions.

View larger version (23K): [in a new window]   Fig. 9. The effect of sorption on metal attenuation. Diagrams compare (a) the concentration attenuation of metals which are sorbed with (b) the curves of the same metals without sorption effects.